This invention relates to a method of producing a support for a planographic printing plate, particularly comprising an aluminum plate, of which the surface is roughened, suitable for offset printing plate.
In general, aluminum plates are widely used as supports for a lithographic printing plate. The surface of the aluminum plate is usually roughened for the purpose of the improvement in adhesiveness of a photosensitive layer provided thereon and the improvement in the water retention of nonimage area (the area which receives damping water used during printing and repels oily ink, and is carried by the area wherein the surface of the support is exposed) of the lithographic printing plate produced using the same.
The roughening is called graining, and there are mechanical methods, such as ball graining, wire graining and blush graining, chemical methods and electrochemical methods.
Heretofore, aluminum plate was treated with a combination of a methanical roughening method and an electrochemical method to form a roughened surface suitable as a support for a planographic printing plate, as disclosed in Japanese Patent KOKAI Nos. 54-63902, 63-104890, 3-132395, etc.
However, in the printing plate using the support for a planographic printing plate formed by the above conventional roughing method, scumming reduction (the ability of not adhering ink onto nonimage area) and fill-in reduction (the ability of nonimage area for retaining water) cannot co-exist, and either characteristic was sacrificed, usually the fill-in reduction is insufficient.
Moreover, printing durability (the ability of not separating a photosensitive layer from a support upon printing) is also insufficient.